In the operation of conventional textile machines such as knitting machines and the like, a considerable problem is presented because of the fact that the machine uses a large number of delicate needles operating at high speed. The probability of an individual needle breaking is quite high and, when a needle is broken or damaged such as being bent out of operable position, it introduces a flaw into the fabric. Because the operating area of the machine is necessarily rather inaccessible, the flaw is not noticed until the fabric begins to emerge from the knitting area and this may be somme time later. This means that, not only is it necessary to discard or sell cheaply a substantial part of the knitted fabric, but a substantial portion of the operating time of the knitting machine has been used before it is discovered that it is producing inferior fabric. Since the machines represent a substantial capital investment, non-productive time represents the loss of a portion of the capital investment, so the net cost os saleable fabric is higher.
Attempts have been made in the past to detect broken needles and to shut down the machine when one occurs. However, such attempts have ended in failure because of the high expense of adequate equipment to perform the operation and because the means of doing so have been complicated. Furthermore, shutdown due to false alarms (i.e., a signal erroneously indicating a defective needle) also causes lost productive time. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a detecting apparatus for a textile or knitting machine which is sensitive in operation, so that it can detect a small change in the shape position or breakage of a needle.
Another object of this invention is the provision of a detecting apparatus for a textile machine such as a kitting machine, which apparatus can be applied to existing machines without substantial modification thereof.
A further object of the present invention is the provision of a detecting means for a machine, which means has no mechanical parts to interfere with the knitting operation.
It is another object of the instant invention to provide a detecting apparatus for use in detecting a broken needle in a knitting machine or the like which apparatus is simple in construction, relatively inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.
A still further object of the invention is the provision of a detecting apparatus for a knitting machine or the like which is not subject to malfunction due to the presence of lint and other debris in the working area.
Applicant's previous patent discloses and claims arrangements for detecting a broken or missing or deformed needle in a knitting machine wherein a group of such needles pass in sequence through the field of a sensing coil with the novel sensing and detecting circuits arranged to respond to an anomalous inductance altering condition in the group of needles present at any time within the field of the sensing coil. Thus, a missing needle or a broken needle would be detected for its inductance altering effect resulting from the difference in the amount of metal for the group of needles in the field of the coil and where a bent needle produced a similar inductance alteration the apparatus would detect that. At times the ability of the apparatus of applicant's prior patent to detect and stop the knitting operation upon the absence of a needle was considered to be undesired in that many knitting operations involved the intentional removal of one or mroe needles to alter or otherwise effect the pattern of goods being knit. Accordingly, it would be useful to have apparatus which will detect broken needles and other malfunctioning entities but which would not produce a stop motion response due to the complete absence of a needle.